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docs: add StatsD configuration details for worker container scaling #3261

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docs: add StatsD configuration details for worker scaling
CoderSufiyan Jul 8, 2026
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fix: update dd-trace link to DogStatsD docs and fix DD_AGENT_HOST des…
CoderSufiyan Jul 8, 2026
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24 changes: 23 additions & 1 deletion content/self-hosting/configuration/scaling.mdx
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Expand Up @@ -30,8 +30,30 @@ On very high loads, it may become necessary to apply additional settings that in
For most environments, we recommend to scale the worker containers by their CPU load as this is a straightforward metric to measure.
A load above 50% for a 2 CPU container is an indicator that the instance is saturated and that the throughput should increase by adding more containers.

In addition, the Langfuse worker also publishes queue length metrics via statsd that can be used to scale the worker containers.
In addition, the Langfuse worker also publishes queue length metrics via StatsD (DogStatsD format) that can be used to scale the worker containers.
`langfuse.queue.ingestion.length` is the main metric that we use to make scaling decisions.

#### Configuring StatsD

Langfuse uses the [`dd-trace`](https://docs.datadoghq.com/developers/dogstatsd/?tab=nodejs) package (DataDog's tracing library) which includes a DogStatsD client. The client auto-configures using standard DataDog environment variables:

| Environment Variable | Default | Description |
| ----------------------- | ------------- | ------------------------------------------ |
| `DD_AGENT_HOST` | `localhost` | DataDog Agent hostname or IP (must run a DogStatsD listener) |
| `DD_DOGSTATSD_PORT` | `8125` | DogStatsD server port |
| `DD_ENV` | — | Environment tag applied to all metrics |
| `DD_SERVICE` | — | Service name tag applied to all metrics |

These variables apply to both the web and worker containers.

Langfuse-specific queue metric configuration (worker container only):

| Environment Variable | Default | Description |
| ---------------------------------------------- | -------- | -------------------------------------------------------------- |
| `LANGFUSE_QUEUE_METRICS_ENABLED` | `true` | Master toggle for publishing queue metrics via StatsD |
| `LANGFUSE_QUEUE_METRICS_INTERVAL_MS` | `1000` | Poll interval for queue depth metrics (minimum 100ms) |
| `LANGFUSE_QUEUE_METRICS_SAMPLE_RATE` | `0.3` | Probability for recording sharded queue depth metrics (0-1) |

The queue metrics can also be published to AWS CloudWatch by setting `ENABLE_AWS_CLOUDWATCH_METRIC_PUBLISHING=true` to configure auto-scalers based on AWS metrics.

### Reducing ClickHouse reads within the ingestion processing
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